class Solution {
public:
    int numDecodings(string s) {
        int n = s.size();
        vector<int> dp(n + 1, 0);

        dp[0] = 1;
        dp[1] = s[0] != '0';

        for (int i = 2; i <= n; ++i)
        {
            if (s[i - 1] >= '1' && s[i - 1] <= '9') dp[i] += dp[i - 1];

            int tmp = (s[i - 2] - '0') * 10 + (s[i - 1] - '0');
            if (tmp >= 10 && tmp <= 26) dp[i] += dp[i - 2];
        }

        return dp[n];
    }
};